1. Field of the Invention
The present invention relates to a method for regulating scanning sample surface charge regulation during wafer inspection or review.
2. Background of the Related Art
Integrated circuit fabrication process uses various types of techniques, such as etching, deposition, and photolithography. Defects often introduced during those processes. Thus, semiconductor integrated circuit need to be inspected and defect need to be reviewed during the fabrication. Regulation of charging status on wafer surface is often needed for charged particle beam inspection and review tools.
Unbalanced charging on wafer surface can adversely affect subsequent fabrication, inspection or defect review processes. To reduce the adverse effects, a conventional pre-charging technique has been developed for SEM defect inspection and review. The pre-charging technique uses a flood gun to create strong and equalized charging on a substrate and its associated structure. The charging can reduce or eliminate the non-uniform distribution of electrostatic charges generated prior to and/or during the e-beam inspection or defect review. But the pre-charging technique may result in image distortions in gray scale, reduced image sensitivity and resolution, and time-dependent location-related differences due to non-uniform charge leakage.
Additionally, to reduce the adverse effect on fabrication or inspection processes, some conventional techniques have been developed to remove electrical charges. These conventional techniques include ionizer radiation and ultraviolet (UV) illumination. The ionizer radiation generates ionized air or gas molecules under the primary electron beam to neutralize electrostatic charges on wafer surface. But the ionizer air/gas under the primary electron beam can (1) lower image resolution and (2) hurt the high vacuum environment in primary beam column. Another conventional technique uses UV illumination. However, the irradiated semiconductor substrate often includes grounded conductive traces and the UV illumination technique usually cannot effectively neutralize electric charges far away from conductive traces.
Hence it is highly desirable to improve techniques for removing and neutralizing electrical charges on wafer surface, especially for e-beam wafer/photo mask inspection and defect review tools.